1. Field of the Invention
The present invention relates to cosmetic brushes. More particularly, it relates to cosmetic brushes with bristles extending radially from a twisted wire core. In particular, it relates to mascara brushes made with shape memory polymer bristles.
2. Description of the Prior Art
Cosmetic brushes having a twisted wire core are known, such as, for example, mascara brushes used to apply mascara to a user's eyelashes. A typical mascara brush is comprised of a core formed from a metallic wire folded in a generally unshaped configuration to provide a pair of parallel segments or lengths of wire. Bristles (also referred to as filaments or fibers), usually comprised of discrete strands of nylon or other synthetic material, are disposed between a portion of the lengths of the wire segments. The wire segments are then twisted, or rotated, about each other to form a helical core (also known as a twisted wire core) which grips the filaments medially of their outer ends, usually substantially at their midpoints, so as to clamp them. In this way, a bristle portion or bristle head is formed with radially extending bristles secured in the twisted wire core in a helical or spiral manner. See, for example, U.S. Pat. No. 4,887,622 to Gueret, and U.S. Pat. No. 4,733,425 to Hartel et al. Each patent cited herein is incorporated by reference in its entirety.
To apply mascara to a user's eyelashes, a brush must be capable of picking up and transporting a supply of mascara from a reservoir and depositing it on a user's eyelashes. Generally, a mascara applicator is inserted into a container having a reservoir of mascara or some other cosmetic product. The bristles are arranged so as to pick up a supply of mascara or product and carry it from the container for application to a user's eyelashes. See, for example, U.S. Pat. No. 4,365,642 to Costa, U.S. Pat. No. 4,733,425 to Hartel et al., and U.S. Pat. No. 4,887,622 to Gueret.
Mascara applicators are preferred that optimize, for example, a combination of loading, application and combing characteristics. Loading refers to the capacity of the applicator to carry product such as mascara. Brushes that maximize loading minimize the number of times a user must introduce the applicator into the reservoir to replenish the supply of mascara product carried on the brush. Application refers to the ability of the brush to deposit product, e.g., mascara, onto a selected site, e.g., eyelashes. Application characteristics are optimized in an applicator that, for example, deposits sufficient quantities of mascara to eyelashes in a uniform and attractive manner and in as few strokes as possible. Combing refers to the ability of a brush to remove clumps by doctoring mascara already applied to lashes and separating lashes that are stuck together. Combing characteristics are optimized in an applicator that properly separates the lashes and distributes or removes excess mascara to provide a finished appearance.
A brush that maximizes loading may have application and combing characteristics that are less satisfactory. For example, a heavily loaded brush may apply excess cosmetic to the eyelashes, thus requiring extra application or combing strokes to remove the excess. Conversely an applicator that applies product or combs lashes with minimal strokes to achieve a finished appearance may carry an insufficient load of product. Accordingly, an ideal applicator optimizes a combination of loading, application and combing characteristics, so that a finished appearance may be expeditiously accomplished in as few strokes as possible and with as few introductions of the applicator into the mascara reservoir as possible.
It is known that providing a bristle head with bristles or fibers of different lengths can improve the loading, application and combing characteristics of a mascara brush. The shorter bristles are believed to improve loading and application characteristics of the brush, while the longer bristles are believed to improve combing characteristics of the brush. For example, a bristle portion of a brush can be trimmed, peripherally, diametrically or linearly, or in any combination of these trim modes. Brushes having bristles trimmed to different lengths are disclosed for example in U.S. Pat. No. 5,595,198 to Kemmerer and U.S. Pat. No. 5,551,456 to Hartel. The brushes disclosed in these references have portions formed from long bristles and portions formed from short bristles. U.S. Pat. No. 5,165,760 to Gueret discloses a method for making a brush comprising shorter stiff bristles and longer soft bristles. The brush is initially made from stiff bristles and soft bristles of the same length. During a grinding operation, the stiff bristles are said to be reduced in length to become the shorter bristles, while the soft bristles are said to deflect sufficiently to avoid the grinder, and remain long. A problem with this method is that pre-determining the length of the long and short bristles with respect to each other relies on the difference in stiffness between the stiff and soft bristles. Accordingly, bristles with a difference in degree of stiffness selected to yield a desired bristle length differential may not exhibit ideal brush characteristics, e.g., combing, loading, application, etc. Conversely, bristles that exhibit ideal brush characteristics may not have a sufficient difference in degree of stiffness to yield an optimal bristle length differential. Furthermore, with the disclosed method, it is not possible to make a brush with short soft bristles interspersed with long stiff bristles, and it is not possible to make a brush with long bristles interspersed with short bristles wherein all of the bristles have a uniform stiffness. These latter two bristle arrangements should yield a more desirable applicator since longer, stiff bristles are believed to provide better combing characteristics, and shorter, soft bristles are thought to provide better application characteristics.
U.S. Pat. No. 6,279,583 discloses a brush that has a twisted wire core supporting a plurality of regularly disposed radially extending short and long bristles. The tips of the long bristles define an outer envelope of the brush. The short and long bristles are interspersed such that tips of the short bristles form a layer spaced inwardly from the outer envelope. The brush can be made without regard to bristle stiffness by first forming a brush blank, initially twisting the wire core only sufficiently to secure the bristles for subsequent steps. The blank is then trimmed to define the length of the short and long bristles, the short bristles defined by cutting a series of circumferentially spaced longitudinal grooves in the bristle envelope of the brush blank. The wire segments are then further twisted to displace and disperse the short bristles among the long bristles such that the tips of the short bristles define a layer spaced inwardly from the tips of the long bristles. A disadvantage of making a brush according to this method is that it requires an additional twisting step after the brush is trimmed to define bristle lengths.
Mascara brushes made with various fiber cross-sections (e.g., tubular, U, I or Z shaped, etc.) are known. Also known are mascara brushes made with curved, kinked or wavy fibers. The various cross-sections and the curved, kinked or wavy fibers are believed to provide advantages over bristles made from round cross-section, straight fibers, such as, for example, improved loading and application characteristics. For example, U.S. Pat. No. 5,161,555 to Cansler discloses a mascara brush utilizing heavily waved bristles instead of straight bristles. However, fibers with unusual cross-sections, and/or curved, kinked, flattened or wavy fibers present special difficulties in production. For example, curved, kinked or wavy fibers are subject to tangling, making it difficult to control during the manufacture of twisted wire core brushes the quantity and orientation of fibers placed between the wire segments prior to twisting. This can lead to significant increases in waste in the form of rejected brush heads due to out-of-specification bristle density and/or bristle orientation.
Accordingly, there is a need for improved mascara brushes and methods of making such brushes that do not suffer the limitations of the prior art brushes and methods.